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Discussion Starter · #1 ·
My car is getting a bad vibration going through the traps. The cage is vibrating bad and shaking.

The set up. (all parts are new)

1987 Buick Grand National
-Moser 12 bolt w/ spool
-Denny's Pro-Mod driveshaft
-HR Parts rear sway bar
-HR adjustable uppers control arms
-HR 1/4" longer lower control arms
-Moog cargo coils (yea, want to put the stock ones back in)
-QA1s set on 5
-15x10 Weld Draglites with 325/50-15 M/T Radials (balanced)

I thought it was the track (Bowling Green) but not after this weekend.

I had the car on the chassis dyno this past Saturday and it did the same thing with the vibration. While strap down, the cage was vibrating real bad at the higher end. When I began turning the rollers, the car was bouncing but it settled down after I got some speed into the rollers.

Where should I begin. Thinking re-balancing the wheels again (easier & cheaper). When I street drive the car, nothing is felt, all is smooth. But then again, I'm not hitting 100+ on the street.

Thanks

Billy T.
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Double check balance of all four wheels/tires.

Check pinion angle. If too excessive, it will cause big vibs at the big end.

Once set to -2 to -4, if vibe is still there, have driveshaft balance checked.
 

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SOFA KING WHAT?
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Double check the yoke on the driveshaft also, make sure it's not butting up against the trans.
 

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Discussion Starter · #6 ·

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yeah rebalance your tires. My car used to vibrate so bad at the big end it was borderline scary. it did the same thing on the chassis dyno. the tires started bouncing. rebalanced the tires the problem went away.
 

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Discussion Starter · #9 ·

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EFI/N2O JUNKIE
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When I pinion angle was bad it vibrated worse the faster I went, really noticed from the 1000ft mark on.....

When I changed it I made it good upstairs but around the pits and return road it was nasty!

Took me awhile to actually learn how to measure and do it correctly. After that it has been perfect! Been 146mph and smooth as silk!
 

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Discussion Starter · #12 ·
After going through the traps and you let off the throttle does the vibration continue, get worse or go away?
It goes away as the speed reduces.

When I brought my wheels to be balanced, there were no weights on the inside of the rim. I originally static balanced them (weights on the inside only). Used the bang on type weights.

This time around, stick on weights were used. The weights were placed on the inside edge and on the backside of the rim face.

The guy that operates the Road Force balancer was off and had to balanced the wheels the common way.

Billy T.
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Discussion Starter · #13 ·
Just an update: Balanced the wheels and fixed the pinion angle.

No vibrations, nice and smooth up to 145mph on radials. Gotta get to the 150mph mark.

Thanks for the advice.

Billy T.
[email protected]
 
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